This year’s tough flu season is now hitting its peak, although there are early signs that the virus activity might be slowing down.

In its weekly FluWatch report, the Public Health Agency of Canada says there were 29,037 laboratory-confirmed cases of flu across the country as of Feb. 3 — nearly 54 per cent attributed to an aggressive H3N2 strain — with more than 3,100 hospitalizations and 130 deaths.

The flu season has been more severe than usual because it involves H3N2, a strain of the influenza A virus that causes more health complications and is more difficult to prevent, health experts say. This strain was responsible for 78 per cent of hospitalizations and deaths. And strikes the hardest (69 per cent) in adults age 65 and older.

It did not help matters that the flu vaccine was a poor match this year, according to data from Australia. A Canadian study made public last week confirmed the dismal performance of the vaccine, whose H3N2 (type A virus) component is about 17 per cent effective in preventing infection. The vaccine portion targeting the type B virus offers 55 per cent protection.

That means that some people who have been vaccinated are nonetheless contracting the flu this season.

Luckily, it’s not the H1N1 virus of 1918 that’s in circulation now, said Alain Gagnon, a Université de Montréal demographer and lead author of a new study that crunched numbers on flu type A, similar to the strain that fuelled the unusually deadly 1918 Spanish flu pandemic that resulted in 50 to 100 million deaths worldwide. At least four other pandemics occurred, although less deadly, including the 1957 H2N2 Asian Flu, the 1968 H3N2 “Hong Kong Flu,” the 1977 Russian Flu and the 2009 H1N1 Swine Flu.

Published last month in mBio, the journal of the American Society for Microbiology, Gagnon’s study provides data to support the hypothesis that previous exposure can build life-long immunity — or paradoxically, leave people vulnerable to the next pandemic for the rest of their lives.

“If it’s the same virus, you should be protected, in most cases,” said Gagnon, head of U de M’s demography department. “Another hypothesis, is that there could be scarring on the lungs during one flu and for the next pandemic, you could be at higher risk.”

The study looked at the number of deaths attributed to flu in the United States and Mexico between 1997 and 2014, and cross-referenced date of birth. Gagnon noted that the study is observational, and further tests are required with animals.

His analysis suggests that people born in 1957 during the time of the Asian Flu pandemic were at a higher risk of dying during the 2009 H1N1 epidemic, as well as the H1N1 outbreak in 2013-2014.

In an earlier study, Gagnon’s team observed that the high death rate of the Spanish Flu that hit a peak with 28-year-olds, was likely due to their exposure to flu in 1889 and 1890.

But the dominant strain this year is H3N2, and some virologists are saying it’s the worst flu season in years, and it’s backed by data.

“In people who are between the ages of 40 and 49, born after the 1968 pandemic, we’ve noticed preliminary data suggesting a lower susceptibility to H3N2 and higher to H1N1,” Gagnon said.

Similarly, those who are 90 years old and older show an inverse ratio, he said. “They were born in the era of H1N1 and have some protection, but were exposed to H3N2 late in life and haven’t built immunity over time, which is why they are more susceptible to that strain,” he said.

For Quebec data, the provincial public health laboratory receives weekly respiratory virus test results from hospitals participating in the provincial sentinel network. The number of tests performed and the number of detected cases diagnosed in the laboratory are then transmitted to the Public Health Agency of Canada.

For Week 5 ending Feb 3, the lab’s data shows a total of 1,271 cases of influenza A, and 1082 cases of influenza B.

Last year for the same five-week period, there were 839 cases of influenza A, and 13 cases of B.

The Quebec Health Department was not able to provide the number of hospitalizations and deaths due to flu.

This Week's Flyers

Comments

Postmedia is pleased to bring you a new commenting experience. We are committed to maintaining a lively but civil forum for discussion and encourage all readers to share their views on our articles. Comments may take up to an hour for moderation before appearing on the site. We ask you to keep your comments relevant and respectful. Visit our Community Guidelines for more information.